Condensate traps are commonly used in steam systems (in which circumstances they are usually referred to as steam traps). Their function is to discharge condensed water from the system, without allowing steam to escape. If steam is lost from the system, this represents a waste of energy. Steam traps thus commonly comprise a valve which is responsive to the presence of condensate or steam in the vicinity of the valve, so that the valve opens when condensate is present and closes when steam is present.